1. Field of the Invention
This invention relates to pleated heat-recoverable wrapping tape.
2. Summary of the Prior Art
The technique of covering substrates, e.g. joints in electrical or telephone cables, with polymeric tape is well-known. Such polymeric tapes include both pressure-sensitive tapes, such as the common electrical tape, and heat-shrinkable tapes, such as those described in U.S. Pat. No. 4,001,065, the disclosure of which is incorporated herein by reference.
Pressure-sensitive tape requires a tight, careful wrapping in order to achieve an adequate seal, while heat-shrinkable tape is less craft-sensitive in that the shrinkage of the tape on heating to its recovery temperature tightens it onto the substrate. When the heat-shrinkable tape is either coated with adhesive, or is self-adhesive at its recovery temperature (as is the tape of U.S. Pat. No. 4,001,065), the seal is more easily formed.
Such heat-shrinkable tapes may include those which have integral heating means, especially those which are electrically self-heatable. Articles of this latter type are described in U.S. Pat. No. 4,177,446 and U.S. patent application Ser. No. 818,711, filed July 25, 1977 and assigned to the assignee of the present invention, the disclosures of which are incorporated herein by reference.
However, when the substrate has a "transition", i.e. it is of non-uniform cross-section, such as when pipes of different diameters have been joined or two telephone cables have been spliced together, in which case the splice area is of greater diameter than the cables, a smooth wrapping is much more difficult to obtain. This smooth wrapping has previously been achieved by the use of narrow tape which is thin and either elastomeric or composed of low yield material, e.g. PVC, so that one edge may be stretched with respect to the other. Narrow tape, however, suffers from a number of disadvantages, in particular:
(1) in order to render it extensible, it is necessarily relatively weak, PA1 (2) because of the narrowness there are many lap areas, and the leak paths, which are generally one-half the tape width, are thus short, PA1 (3) for the above reasons, installation is craft sensitive.